Retroflector having multi-beam antennas with individual ports for individual beams and means interconnecting ports of like directed beams



June 7, 1966 P. w. HANNAN 3,255,457

RETROFLECTOR HAVING MULTI-BEAM ANTENNAS WITH INDIVIDUAL PORTS FORINDIVIDUAL BEAMS AND mans INTERCONNECTING PORTS 0F LIKE DIRECTED BEAMSFiled June 28, 1963 5 Sheets-Sheet 1 INCIDENT WAVE DIRECTION INCIDENT AWAVE FRONT June 7, 1966 P. w. HANNAN 3,2 ,4 7

RETROFLECTOR HAVING MULTI-BEAM ANTENNAS WITH INDIVIDUAL PORTS FORmmvmwu. BEAMS ma MEANS mmncommcwme PORTS 0F LIKE mmacm: BEAMS Filed June28, 1963 5 Sheets-Sheet 2 June 7, 1966 P. w. HANNAN 3,255,457

RETR F ECTOR HAVING IBEAM ANTENNAS WITH INDIVIDUAL PORTS R INDIVIDUALAND I S INTERCONNECTING PORTS KB DIR ED BEAMS Filed June 28, 1963 5Sheets-$heet 3 June 7, 1966 P. w. HANNAN 3,255,457

RETROFLECTOR HAVING MULTI-BEAM ANTENNAS WITH INDIVIDUAL PORTS FORINDIVIDUAL BEAMS AND MEANS INTERCONNECTING PQRTS OF LIKE nmzc'rm BEAMS 5Sheets-Sheet 4.

Filed June 28, 1963 FIG.

June 7, 1966 P. w. HANNAN 3,255,457

RETROFLECTOR HAVING MULTI-BEAM ANTENNAS WITH INDIVIDUAL PORTS FORINDIVIDUAL BEAMS AND MEANS INTERCONNECTING PORTS or LIKE mnncmn BEAMSFiled June 28, 1963 5 Sheets-Sheet 5 FIG. 6

United States Patent RETROFLECTOR HAVING MULTI-BEAM ANTEN- NAS WITHINDIVIDUAL PORTS FOR INDIVID- UAL BEAMS AND MEANS INTERCONNECTING PORTS0F LIKE DIRECTED BEAMS Peter W. Hannan, Northport, N.Y., assignor toHazeltine Research Inc., a corporation of Illinois Filed June 28, 1963,Ser. No. 291,480 15 Claims. (Cl. 343-853) This invention relates toreflecting antenna array systems and, more particularly, to such systemsable to provide a substantially uniform high level of reflection for anyincidence angle, or alternatively, for a range of incidence angles.

There exists a need for an efficient means for enhancing the reflectionof a radio wave from an object. The traditional device employed for thispurpose has been a corner reflector or a cluster of corner reflectors.However, the former has a limited coverage angle, while the latter hasangular regions of low response and interferences.

The essential problems involved in achieving high return of the incidentwaves, together with complete independence of orientation of thereflecting device, may be illustrated by comparing two simple devices.One device, a flat reflecting plate many wave lengths in diameter,achieves very high return when it is broadside to the wave direction,but the return falls off rapidly with departure from the broadsidecondition. The other device, a reflecting sphere, yields a return whichis independent of orientation, but the return is weak compared to thebroadside return of the plate just described.

In recent years, two significant advances have been made in this field.In one case, a Luneberg lens coated with a partially reflecting surfaceachieves high returns independent of orientation. Unfortunately, when alarge lens is required, the great volume and weight of dielectricmaterial needed makes this solution unattractive. In the other case,several Van Atta arrays are grouped together, each operating over adifferent range of angles, so that coverage nearly independent oforientation can be ob tained with a relatively lightweight structure; inaddition, amplifiers or modulators may be employed to achieve somefurther capabilities. Unfortunately, in such arrangements, utilizing VanAtta arrays there exist interference regions at those angles where twoarrays are equally effective. For such regions the reflected signalamplitude is greatly reduced.

It is an object of this invention to provide improved reflecting antennaarray systems which avoid one or more disadvantages of the prior art andwhich allow a high level of reflection independent of incident angles.

It is an additional object of this invention to achieve a combination ofthe desirable performance characteristics of the Luneberg reflector withthose of the Van Atta array system. More particularly, it is an objectto achieve the isotropic performance of the Luneberg reflector, togetherwith the light weight and adaptability of the Van Atta array system.

In accordance with the invention, a reflecting antenna array system forproviding a substantially uniform high level of reflection for anyincidence angle comprises, a plurality of multibeam antennas supportedin a substantially spherical array, each antenna having a separate portfor each of its beams, and a plurality of transmission lines connectedto the ports of the antennas, each port being connected to the portwhich has the same beam direction and which occupies the symmetricalposition relative to the beam direction involved; whereby incident wavesin a range of frequencies are efficiently reflected back toward thesource of these waves.

Also in accordance with the invention, a reflecting antenna array systemfor providing a substantially uniform high level of reflection for anyincidence angle comprises, a plurality of Luneberg-lens antennassupported in a substantially spherical array, each antenna having aplurality of feeds each representing a separate beam, a first group ofshort-circuited transmission lines short circuiting each feed whichcorresponds to a beam direction perpendicular to the array surface and asecond group of transmission lines interconnecting the remaining feeds,each individual feed of each antenna being connected to a single feed ofanother antenna which has the same beam direction and which occupies asymmetrical position relative to the incident wave direction involved;whereby incident waves in a range of frequencies are eflicientlyreflected back toward the source of those waves.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawings, and itsscope will be pointed out in the appended claims.

In the drawings, FIG. 1 shows a particular form of reflecting arraysystem constructed in accordance with the invention;

FIG. 2 shows a modification of the FIG. 1 system allowing operation withany polarization;

FIG. 3 is a simplified drawing used in describing relationships betweenvarious significant parameters and dimensions of systems constructed inaccordance with the invention;

FIG. 4 is a planar projection of a complete spherical reflecting antennaarray system utilizing Luneberg-lens antennas (actually a completesystem is not shown because two portions have been removed due tolimitations in drawing size);

FIG. 5 is a detail view of a portion of the FIG. 4 system, and

FIG. 6 is a partial sectional view along a diameter of the completespherical system of FIG. 4.

FIG. 1 system Referring to FIG. 1, there is shown a view of a portion ofa reflecting antenna array system for providing a substantially uniformlevel of reflection over a range of incidence angles. FIG. 1 shows agroup of antennas supported in a circular array; this simple arrangementwill be discussed to bring out the concepts of the invention beforeconsidering a full spherical array. For the purposes of thisspecification the word port is used as a term generic to the word feed,both words being ap plied in accordance with common usage in the antennaart.

In FIG. 1 are shown seven antennas 10-16, each of which is a multibeamantenna. Examining antenna 13, it will be seen that this antenna hasfive ports labeled 4R, 2R, S, 2L and 4L. Each of these ports has aseparate antenna pattern or beam associated therewith. Thus, beam 18corresponds to port 4R, beam 19 corresponds to port 2R, beam 20corresponds to port S, etc.; the dotted line in the center of each beambeing effectively an extension of the corresponding port. It will benoted that with respect to the remaining antennas -12 and 14-16, onlythe dotted center lines of the beams are shown without a beam contourpattern.

Also shown in FIG. 1 are a plurality of transmission lines connected toports of the antennas. Only three typical transmission line connections21, 22 and 23 are shown for ease of drawing and explanation. Line 21 isa section of transmission line connecting port 4L of antenna to port 4Rof antenna 11. It can now be noted that the 4L and 4R designations arelocation codes. The 4L port of antenna 15 is interconnected to thefourth (4) antenna to the left (L), which is antenna 11; connection mustbe to port 4R of antenna 11 because that is the port of antenna 11 whichcarries the fourth (4) antenna to the right- (R) designation. In similarmanner, port 2L of antenna 14 is connected, via transmission line 22, toport 2R of antenna 12. Port S of antenna 13 is effectively connected toitself by the transmission line 23 which is short circuited at the farend. All the connections between the antennas shown in FIG. 1 (as wellas to the additional antennas which could be added to form a completecircle) can now be made following the location code designations.

Assuming now that an electromagnetic wave approaches the FIG. 1 systemwith a plane wave front indicated by the straight line labeled IncidentWave Front and a direction indicated by the arrow labeled Incident WaveDirection. Such a wave will be intercepted by antennas having beams ofdirection approximately corresponding to the incident wave direction.This condition of corresponding direction is met in FIG. 1 by the beamsassociated with port 4L of antenna 15, port 2L of antenna 14, port S ofantenna 13, port 2R of antenna 12 and port 4R of antenna 11. Signalsoriginating from the vicinity of point 24 in the incident wave will becoupled, via the combination of port 4L of antenna 15, line 21 and port4R of antenna 11, to the vicinity of point 28. Similarly, signalsoriginating near point 25 will be coupled to the vicinity of point 27,signals originating near point 26 will be coupled back to the vicinityof point 26, signals originating near point 27 will be coupled to thevicinity of point 25 and signals originating near point 28 will becoupled to the vicinity of point 24. The result will be a reconstitutedwave travelling away from the reflecting array system.

If the lengths of the transmission lines 21, 22 and 23 are chosen sothat the electrical path lengths from point 24 to point 28, from point25 to point 27 and from point 26 back to point 26, are all substantiallyidentical, then the reconstituted wave will have a plane wave frontcorresponding to the plane wave front of the incident wave. The netresult will be that the incident wave is efliciently reflected backtoward the original source of the waves. If desired, the incident wavecan be effectively defocused prior to being reconstituted by choosingthe lengths of lines 21, 22 and 23 so that the path lengths are unequal(instead of substantially identical as just discussed). Such defocusingwill cause the wave power to be returned over a solid angle centered onthe original source of the wave with correspondingly reduced strength.

The arrangement as shown in FIG. 1 will be defined as one in which eachport of the system is connected, via a transmission line, to the portwhich has the same beam direction and which occupies the symmetricalposition relative to the beam direction involved. Thus, in FIG. 1, thebeam direction involved is the direction corresponding to the incidentwave direction. The ports corresponding to this particular beamdirection are port 4L of antenna 15, port 2L of antenna 14, port S ofantenna 13, port 2R of antenna 12 and port 4R of antenna 11. Each ofthese ports is interconnected, as shown, to the port which occupies thesymmetrical postion relative to this particular beam direction. Moreparticularly, the FIG. 1 system includes two types of transmissionlines. The first group of transmission lines, of which line 23 istypical, are short circuited. The short-circuited ports are the portswhich correspond to a beam direction perpendicular to the array surface.Thus, port S of antenna 13 corresponds to beam 20 which is substantiallyperpendicular to the array surface. With respect to port S of antenna13, this port itself occupies the symmetrical position and iseffectively coupled back to itself via the short-circuited line 23. Thesecond group of transmission lines, of which lines 21 and 22 aretypical, interconnect the remaining ports which are not connected toshort-circuited lines. As described above, this is typicallyaccomplished by interconnecting port 4L of antenna 15 and port 4R ofantenna 11, since these two ports occupy symmetrical positions relativeto their beam directions.

It will be understood that any suitable type of multibeam antennas canbe utilized in systems constructed in accordance with the invention. Oneparticular type of antenna will be described in connection with the FIG.4 arrangement.

FIG. 2 system In the FIG. 1 arrangement each beam direction of eachantenna has a single port and the system can be designed to operate forany one particular polarization. FIG. 2 shows a portion of the FIG. 1arrangement modified for operation with any polarization. Each FIG. 2antenna 12', 13 and 14 has five pairs of ports, each pair covering twoorthogonal wave polarizations. Each antenna has a separate port for eachof its beams and two beams for orthogonal polarizations for each beamdirection. For example, one port of each pair may be for verticalpolarization and the other for horizontal polarization. Thus, for thebeam direction indicated, ports 2LH and 2LV of antenna 14', and portsZRH and 2RV of antenna 12' are involved. The beams for the vertical andhorizontal polarizations are substantially identical so that only onebeam contour is shown for each of these pairs of ports. Thesedesignations ZLH, 2LV, etc. are location codes the same as discussedabove with the addition of the V and H designations corresponding tovertical and horizontal polarizations, respectively. As shown, each portwill again be connected to the port which has the same beam directionand which occupies the symmetrical position relative to the beamdirection involved. However, in this case two transmission lines areutilized for each beam direction so that each port is connected to therespective port of the proper polarization.

In operation, an incident wave with a linear polarization correspondingto arrow 30 will be separated into two orthogonal components with thevertical component utilizing line 32 and the horizontal componentutilizing line 33 so that the reflected wave will have a polarizationcorresponding to arrow 31, which is the same polarization as indicatedby arrow 30. Similarly as in FIG. 1, ports corresponding .to beamdirections perpendicular to the array surface will have each portshort-circuited by shortcircuited lines such as 34 and 35.

While an incident wave of any linear polarization will be reflected as awave of the same polarization by the FIG. 2 arrangement, an incidentwave of circular polarization will be reflected as a wave of theopposite circular polarization. This is the well known reversal whichoccurs with any single simple reflection of a circularly-polarized wave.It might be desired that an infient circularly polarized wave bereturned without polarization reversal. This can be accomplished in theFIG. 2 arrangement merely .by interchanging the interconnections betweenthe two ports of each beam direction. That is by connecting the lowerend of line 32 to port ZRH of antenna 12 and the lower end of line 33 toport ZRV of antenna 12'. Also, the lines 34 and 35 will be connectedtogether at the free ends instead of being individually short circuited.This interchanging of the port connections would, of course, have theadditional effect of rotating the polarization of any linearly polarizedwave by 90. An alternate way to achieve the results described wouldemploy ports corresponding to circularly-polarized waves. -In this casethe rules for interchanging connections are opposite to those withlinear polarization.

FIG. 3 system In FIG. 3 and below are indicated various significantparameters and dimensions associated with systems constructed inaccordance with the present invention:

D=sphere diameter d=antenna aperture diameter A=design wavelengthp=half-power beamwidth of an antenna aperture =angle of effectiveantennas on sphere n=number of beams per aperture beamwidth P=number ofantennas on sphere Q=number of beams in one antenna; Q also equals thenumber of active antennas S=total number of feeds k=ratio of highestusable frequency to lowest usable frequency The following are certainimportant relationships be tween the above parameters and dimensions:

9% LEN x 2n A fi D D a '7 D P 8n d: D Q Sn sin (4) 1 2 2 S-[8n sin IIThe above relationships are based on the assumption of a sphere manywavelengths in diameter, which is the condition for eflicient and usefuloperation of the invention. It can be seen that the diameter of theindividual antennas is proportional to the geometric mean of the designwavelength and the sphere diameter. Also, the total number oftransmission lines is proportional to the square of the ratio of spherediameter to design wavelength (this is similar to the result for a VanAtta array). Although wavelength appears as a parameter in the formulas,the system is not necessarily narrow band. As wavelength is varied in agiven system, the number (n) of ports per antenna beamwidth varies. Aslong as the ports per beamwidth is one or more, and the beamwidth (B) issmall compared with the sphere surface angle (4)), the system willperform well; i.e., a sphere diameter very large in wavelengths permitsoperation over a wide frequency band.

As described, the system provides a high return which is independent ofpolarization. When all the ports corresponding to all the beamdirections are connected up, and when a sufliciently large number ofantennas and beams are employed, the return is essentially independentof orientation of the system, and exhibits no significant interferences.The resulting performance is thus similar to that of the isotropicLuneberg reflector. However, since each antenna may be relatively smalland light, and since the antennas are connected with transmission lines,those advantages associated with the Van Atta array are also achieved.

6 System of FIGS. 4, 5 and 6 FIGS. 4, 5 and 6 show a specific design ofan array system constructed in accordance with the invention utilizing alarge number of Luneberg-lens antennas. FIG .4 is a projection of thecomplete surface of a spherical reflecting antenna array system(actually two portions are missing, as will be noted below). FIG. 4 maybe likened to a type of polar projection of the surface of the earthrelied upon in certain maps. It will be appreciated that no planarrepresentation of a spherical surface will be completely accurate. Thesurface of one hemisphere of the spherical array system is includedwithin the pentagon labeled 40. The other hemisphere comprises fiveidentical, approximately pie-shaped pieces, of which three are shown andtwo have been omitted to avoid crowding in the drawing. The dot-dashline labeled AA represents a diameter of the complete spherical arraysystem.

The array system illustrated in FIG. 4 includes three slightly differenttypes of antennas: antennas such as 41, which are spaced away from allother antennas; antennas such as 42, which are surrounded by a clusterof five other antennas in close proximity; and antennas such as 43, fiveof which cluster around each type 42 antenna. The whole spherical arraycomprises a regular pattern of these three types of antennas. Thecomplete group of antennas lying along the diameter AA are labeled41-52, inclusive. FIG. 5 is an enlarged view of antennas 41, 42 and 43and a few neighboring antennas. Each Luneberg-lens antenna is shown asbeing optically transparent and having a plurality of feeds coupled toits far surface. In each antenna 41, 42 and 43, the feeds which liealong the diameter AA are numbered. Thus, of the thirteen feeds ofantenna 41, the three lying along diameter AA are labeled 55, 56 and 57.Of the sixteen feeds of antenna 42, the four lying along diameter AA arelabeled 58, 59, 60 and 61. Of the thirteen feeds of antenna 43, thethree lying along the diameter A-A are labeled 62, 63 and 64. In FIG. 6is shown a side sectional view of the antennas 41-52 which lie alongdiameter AA. In FIG. 6, diameter AA is represented by means which is themechanical structure which supports the antennas in the sphericalconfiguration; any appropriate physical arrangement can be utilized tosupport the antennas as described.

Considering FIGS. 4, 5 and 6 together, there is shown a reflectingantenna array system for providing a substantially uniform high level ofreflection for any incidence angle. As illustrated, the system includesa plurality of multibeam antennas, shown as Luneberg-lens antennas ofwhich 41, 42 and 43 are typical, supported in a substantially sphericalarray. Each antenna has a separate feed (such as feeds 55-74, forexample) for each of its beams, and each feed is shown as having twoports for orthogonal polarizations. As illustrated, the system furtherincludes a plurality of transmission lines (four representative linesare labeled 81-84) connected to the feeds of the antennas, each feedbeing connected to the feed which occupies the symmetrical positionrelative to the beam direction involved (in the manner discussed morefully with reference to FIG. 1). More particularly, there are shown afirst group of short-circuited transmission lines, of which lines 83 and84 are examples, short circuiting each port of each feed whichcorresponds to a beam direction perpendicular to the array surface. Alsoincluded are a second group of transmission lines, of which lines 81 and82 are examples, interconnecting the ports of the remaining feeds.

In the system shown, an over-all spherical diameter (D) of about twelvewavelengths, a Luneberg-lens antenna diameter (d) of about twowavelengths and an average sphere-surface angle of about were chosen.The total number of individual antennas utilized in this arrangement isninety-two, which is suflicient to yield a strong return and nearlyisotropic coverage. The total number of feeds in this arrangement asshown is 1,232, which amounts to approximately one feed per antennabeamwidth for this system. The resulting system will provide a highlevel of reflection from a light-weight and versatile device,independent of incidence angle.

In accordance with the invention, reflecting array systems can beconstructed in a substantially spherical configuration or in a partialspherical configuration (for example, a hemispherical configuration) forproviding a substantially uniform high level of reflection over a rangeof incidence angles rather than for all incidence angles.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed to cover all such changes and modifications as fall within thetrue spirit and scope of the invention.

What is claimed is:

1. A reflecting antenna array system for providing a substantiallyuniform high level of reflection for any incidence angle, comprising:

a plurality of multibeam antennas supported in a substantially sphericalarray, each antenna having a separate port for each of its beams;

and a plurality of transmission lines connected to said ports of saidantennas, each port being connected to that port which has the same beamdirection and which occupies the symmetrical position relative to thebeam direction involved;

whereby incident waves in a range of frequencies are efficientlyreflected back toward the source of said waves.

2. A reflecting antenna array system for providing a substantiallyuniform high level of reflection over a range of incidence angles,comprising:

a plurality of multibeam antennas supported in a partial sphericalarray, each antenna having a separate port for each of its beams;

and a plurality of transmission lines connected to said ports of saidantennas, each port being connected to the port which has the same beamdirection and which occupies the symmetrical position relative to thebeam direction involved;

whereby incident waves in a range of frequencies are efiicientlyreflected back toward the source of said waves.

3. A reflecting antenna array system for providing a substantiallyuniform high level of reflection for any incidence angle, comprising:

a plurality of multibeam antennas supported in a substantially sphericalarray, each antenna having a separate port for each of its beams;

a first group of short-circuited transmission lines short circuitingeach port which corresponds to a beam direction perpendicular to thearray surface;

and a second group of transmission lines interconnecting the remainingports, each individual port of each antenna being connected to a singleport of another antenna which has the same beam direction and whichoccupies the symmetrical position relative to the incident wavedirection involved;

whereby incident waves in a range of frequencies are efficientlyreflected back toward the source of said waves.

4. A reflecting multibeam antenna array system for providing asubstantially uniform high level of reflection for any incidence angle,comprising:

a plurality of multibeam antennas supported in a substantially sphericalarray, each antenna having a separate port for each of its beams;

a first group of short-circuited transmission lines short circuitingeach port which corresponds to a beam direction perpendicular to thearray surface;

and a second group of transmission lines interconnecting the remainingports, each individual port of each antenna being connected to a singleport of another antenna which has the same beam direction and whichoccupies the symmetrical position relative to the incident wavedirection involved;

the lengths of said transmission lines of said first and second groupsbeing such that the electrical path length from an incident plane wavefront, through the array and back to the wave front is approximatelyidentical for all paths corresponding to a beam direction substantiallyperpendicular to said wave front;

whereby incident waves in a range of frequencies are eflicientlyreflected back toward the source of said waves.

5. A reflecting multibeam antenna array system for providing asubstantially uniform level of reflection over a range of incidenceangles, comprising:

a plurality of multibeam antennas supported in a partial sphericalarray, each antenna having a separate port for each of its beams;

and a first group of short-circuited transmission lines short circuitingeach port which corresponds to a beam direction perpendicular to thearray surface;

and a second group of transmission lines interconnecting the remainingports, each individual port of each antenna being connected to a singleport of another antenna which has the same beam direction and whichoccupies the symmetrical position relative to the incident wavedirection involved;

the lengths of said transmission lines of said first and second groupsbeing such that the electrical path length from an incident plane wavefront, through the array and back to the wave front is approximatelyidentical for all paths corresponding to a beam direction substantiallyperpendicular to said wave front;

whereby incident waves in a range of frequencies are efficientlyreflected back toward the source of said waves.

6. A reflecting multibeam antenna array system for providing asubstantially uniform high level of reflection for any Incidence angle,comprising:

a plurality of multibeam antennas supported in a substantially sphericalarray, each antenna having a separate port for each of its beams and twobeams for orthogonal polarizations for each beam direction;

a first group of short-circuited transmission lines short c rcuitingeach port which corresponds to a beam direction perpendicular to thearray surface;

and a second group of transmission lines interconnectmg the remainingports, each individual port of each antenna being connected to a singleport of another antenna which has the same beam direction and WhJChoccupies the symmetrical position relative to the incident wavedirection involved;

whereby incident waves in a range of frequencies are eflicientlyreflected back toward the source of said waves.

7. A reflecting antenna array system for providing a substantiallyuniform level of reflection over a range of incidence angles,comprising:

a plurality of multibeam antennas supported in a partial sphericalarray, each antenna having a separate port for each of its beams and twobeams for orthogonal polarizations for each beam direction;

a first group of short-circuited transmission lines short circuitingeach port which corresponds to a beam direction perpendicular to thearray surface;

and a second group of transmission lines interconnecting the remainingports, each individual port of each antenna being connected to a singleport of another antenna which has the same beam direction and whichoccupies the symmetrical position relative to the incident wavedirection involved;

whereby incident waves in a range of frequencies are eflicientlyreflected back toward the source of said waves. 8. A reflecting antennaarray system for providing a substantially uniform high level ofreflection for any incidence angle, comprising:

a plurality of Luneberg-lens antennas supported in a substantiallyspherical array, each antenna having a purality of feeds eachrepresenting a separate beam;

and a plurality of transmission lines connected to said feeds of saidantennas, each feed being connected to the feed which has the same beamdirection and which occupies the symmetrical position relative to thebeam direction involved;

whereby incident waves in a range of frequencies are eflicientlyreflected back toward the source of said waves.

9. A reflecting antenna array system for providing a substantiallyuniform high level of reflection for any incidence angle, comprising:

a plurality of Luneberg-lens antennas supported in a substantiallyspherical array, each antenna having a plurality of feeds eachrepresenting a separate beam;

a first group of short-circuited transmission lines short circuitingeach feed which corresponds to a beam direction perpendicular to thearray surface;

and a second group of transmission lines interconnecting the remainingfeeds, each individual feed of each antenna being connected to a singlefeed of another antenna which has the same beam direction and whichoccupies the symmetrical position relative to the incident wavedirection involved;

whereby incident waves in a range of frequencies are efficientlyreflected back toward the source of said waves.

10. A reflecting antenna array system for providing a substantiallyuniform high level of reflection for any incidence angle, comprising:

a plurality of Luneberg-lens antennas supported in a substantiallyspherical array, each antenna having a plurality of feeds eachrepresenting a separate beam;

a first group of short-circuited transmission lines short circuitingeach feed which corresponds to a beam direction perpendicular to thearray surface;

and a second group of transmission lines interconnecting the remainingfeeds, each individual feed of each antenna being connected to a singlefeed of another antenna which has the same beam direction and whichoccupies the symmetrical position relative to the incident wavedirection involved;

the lengths of said transmission lines of said first and second groupsbeing such that the electrical path length from an incident plane wavefront through the array back to the wave front is approximatelyidentical for all paths corresponding to a beam direction substantiallyperpendicular to said wave front;

whereby incident waves in a range of frequencies are eflicientlyreflected back toward the source of said waves.

11. A reflecting antenna array system for providing a substantiallyuniform high level of reflection for any incidence angle, comprising:

a plurality of Luneberg-lens antennas supported in a substantiallyspherical array, each antenna having a plurality of feeds eachrepresenting a separate beam and two beams for orthogonal polarizationsfor each beam direction;

and a plurality of transmission lines connected to said feeds of saidantennas, each feed being connected to the feed which has the same beamdirection and which occupies the symmetrical position relative to thebeam direction involved;

whereby incident waves in a range of frequencies are eflicientlyreflected back toward the source of said waves.

12. A reflecting antenna array system for providing a substantiallyuniform high level of reflection for any incidence angle, comprising:

a plurality of Luneberg-lens antennas supported in a substantiallyspherical array, each antenna having a plurality of feeds eachrepresenting a separate beam and two beams for orthogonal polarizationsfor each beam direction;

a first group of short-circuited transmission lines short circuitingeach feed which correspond to a beam direction perpendicular to thearray surface;

and a second group of transmission lines interconnecting the remainingfeeds, each individual feed of each antenna being connected to a singlefeed of another antenna which has the same beam direction and whichoccupies the symmetrical position relative to the incident wavedirection involved;

the lengths of said transmission lines of said first and second groupsbeing such that the electrical path length from an incident plane wavefront, through the array and back to the wave front is approximatelyidentical for all paths corresponding to a beam direction substantiallyperpendicular to said wave front;

whereby incident waves in a range of frequencies are eflicientlyreflected back toward the source of said waves.

13. A polarization changing reflecting antenna array system forproviding a substantially uniform high level of reflection for anyincidence angle, comprising:

a plurality of multibeam antennas supported in a substantially sphericalarray, each antenna having a separate port for each of its beams and twobeams for orthogonal polarizations for each beam direction;

and a plurality of transmission lines connected to said ports of saidantennas, each port being connected to the port which has the same beamdirection and which occupies the symmetrical position relative to thebeam direction involved with the port connections interchanged toproduce a change in polarization between incident and reflected waves;

whereby incident waves in a range of frequencies are efficientlyreflected back toward the source of said waves with a change inpolarization so that incident waves of one linear polarization arereflected as waves of an orthogonal linear polarization and waves of afirst circular polarization are reflected as waves of the same circularpolarization.

14. A polarization changing reflecting antenna array system forproviding a substantially uniform high level of reflection for anyincidence angle, comprising:

a plurality of Luneberg-lens antennas supported in a substantiallyspherical array, each antenna having a plurality of feeds eachrepresenting a separate beam and two beams for orthogonal polarizationsfor each beam direction;

and a plurality of transmission lines connected to said feeds of saidantennas, eac-h feed being connected to the feed which has the same beamdirection and which occupies the symmetrical position relative to thebeam direction involved with the feed connections interchanged toproduce a change in polarization between incident and reflected waves;

whereby incident waves in a range of frequencies are efficientlyreflected back toward the source of said waves with a change inpolarization so that incident waves of one linear polarization arereflected as waves of an orthogonal linear poralization and waves of afirst circular polarization are reflected as waves of the same circularpolarization.

15. A polarization changing reflecting antenna array system forproviding a substantially uniform high level of reflection for anyincidence angle, comprising:

a plurality of Luneberg-lens antennas supported in a substantiallyspherical array, each antenna having a plurality of feeds eachrepresenting a separate whereby incident waves in a range of frequenciesare beam and two beams for orthogonal polarizations for each beamdirection;

and a plurality of transmission lines connected to said feed of saidantennas, each feed being connected to efliciently reflected back towardthe source of said wave with a change in polarization so that incidentwaves of one linear polarization are reflected as waves of an orthogonallinear polarization and waves the feed which has the same beam directionand which occupies the symmetrical position relative to the beamdirection involved with the feed connections interchanged to produce achange in polarization of a first circular polarization are reflected aswaves of the same circular polarization.

References Cited by the Examiner between incident and I'CfifiCtCd waves;10 STATES PATENTS the lengths of said transmission lines being such thatthe electrical path length from an incident plane 2'566703 9/1951 Iams343-753 wave front, through the array and back to the wave 2'908'00210/1959 van Ana 343'776 front is approximately identical for all pathscorresponding to a beam direction substantially perpen- 15 dicular tosaid wave front;

HERMAN KARL SAALBACH, Primary Examiner. R. F. HUNT, Assistant Examiner.

1. A REFLECTING ANTENNA ARRAY SYSTEM FOR PROVIDING A SUBSTANTIALLYUNIFORM HIGH LEVEL OF REFLECTION FOR ANY INCIDENCE ANGLE, COMPRISING: APLURALITY OF MULTIBEAM SUPPORTED IN A SUBSTANTIALLY SPHERICAL ARRAY,EACH ANTENNA HAVING A SEPARATE PORT FOR EACH OF ITS BEAMS; AND APLURALITY OF TRANSMISSION LINES CONNECTED TO SAID PORTS OF SAID ANTENNA,EACH PORT BEING CONNECTED TO THAT PORT WHICH HAS THE SAME BEAM DIRECTIONAND WHICH OCCUPIES THE SYMMETRICAL POSITION RELATIVE TO THE BEAMDIRECTION INVOLVED; WHEREBY INCIDENT WAVES IN A RANGE OF FREQUENCIES AREEFFICIENTLY REFLECTED BACK TOWARD THE SOURCE OF SAID WAVES.